`_framework/blazor-hotreload` 404 when running under subdirectory

[crackalak]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Please note: This is not the same as the 404 for blazor-hotreload.js, which has been fixed with #36897, but this is the second part of #35555 which I believe was missed.

The fetch request for _framework/blazor-hotreload from blazor-hotreload.js returns 404 due to the url being relative to the subdirectory, contents of blazor-hotreload.js:

export function receiveHotReload() {
  return BINDING.js_to_mono_obj(new Promise((resolve) => receiveHotReloadAsync().then(resolve(0))));
}

async function receiveHotReloadAsync() {
  const cache = window.sessionStorage.getItem('blazor-webassembly-cache');
  let headers;
  if (cache) {
    headers = { 'if-none-match' : cache.etag };
  }
  const response = await fetch('_framework/blazor-hotreload', { headers });
  if (response.status === 200) {
    const deltas = await response.json();
    if (deltas) {
      try {
        deltas.forEach(d => window.Blazor._internal.applyHotReload(d.moduleId, d.metadataDelta, d.ilDelta));
      } catch (error) {
        console.warn(error);
        return;
      } 
    }
  }
}

Expected Behavior

blazor-hotreload should load successfully and hot reload should work

Steps To Reproduce

1. Create a hosted ASP.NET Core + Blazor WebAssembly Project
2. Configure it to operate under a subdirectory (set base href, StaticWebAssetBasePath etc)
3. Run the hosted project.
4. Observe that blazor-hotreload.js loads correctly but requests _framework/blazor-hotreload (relative to the subdirectory), breaking hot reload.

Repro: https://github.com/crackalak/BlazorHotReload404

Exceptions (if any)

No response

.NET Version

6.0.201

Anything else?

[javiercn]

@crackalak thanks for contacting us and for the detailed analysis.

I believe this is a bug.

Thanks for contacting us.

We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[javiercn]

For reference, all this code lives https://github.com/dotnet/sdk/tree/ea952247b79d17013e89c9b5ec82f1d6db830216/src/BuiltInTools/BrowserRefresh